Why when I send an SMS do my credits not deduct straight away

We queue your messages for delivery, if there is an error sending your SMS message to a client, then an SMS credit is not deducted. We only deduct credits once the SMS is pushed to the provider. If you send more SMS's than you have credits, then your SMS's will get queued until you recharge your SMS credit balance. These SMS's will be stored for a period of time before expiring.